Problem: $ { {-4} \times \left[\begin{array}{r}{-1} \\ {2} \\ {3}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{-4}\times{-1} \\ {-4}\times{2} \\ {-4}\times{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{4} \\ {-8} \\ {-12}\end{array}\right]}$